The efficiency of an ozonation process in the degradation of the Kraft E-1 effluent was evaluated. The investigation was focused on the reduction of chemical oxygen demand, total phenols, color and the absorbance at 254 nm. The chronic toxicity was evaluated by growth inhibition of algae Selenatrum capricornutum and cytotoxicity evaluation of effluents samples by determination of the nucleic acid content (NCA) endpoint. After 60 minutes of ozonation, COD and UV254 only reached 21% and 34% efficiency reduction. Total phenols and color were more rapidly removed ( at 10 minutes of treatment). The results showed that the chronic toxicity (Selenastrum capricornutum algae) decreases for all effluent doses studied. The cytotoxicity assay indicated that toxic compounds were not generated by the ozonation process.2914753